A case of generalized P. carinii infection is reported where severe hypoalbuminemia developed shortly before death. The patient, a 54 year old male, felt extremely weak during more than a year and then developed pulmonary symptoms (cough, expectoration, fever). Because of radiological suspicion of a pulmonary cyst or abscess, a lobectomy was performed. Microscopic examination revealed P. carinii pneumonia. Five months later he died from generalized P. carinii infection. At autopsy, numerous small abscesses were found in which the pneumocyst could be demonstrated. Hypopro-teinemic edema developed 2 months before death. An extreme hypoalbuminemia was present (serum albumin 0.2-0.4 g/100 ml) and a strongly reduced serum concentration of IgG-globulin (5% of normal mean), whereas the serum concentration of the immunoglobulins IgA and IgM was normal. Thus, the primary disease was probably hypo-or agammaG-globulinemia, which is known, in particular in children, to predispose to P. carinii infection. Using 125I-albumin, a greatly increased turnover rate of albumin was demonstrated, as in protein-losing diseases. However, no abnormal loss of plasma protein could be detected, in particular none in the gastrointestinal tract (normal 59Fe-iron dextran test). It is suggested that the pneumocysts produce enzymes which split albumin when the pneumocysts are present in large number. However, this mechanism of the "hypercatabolic" hypoalbuminemia remains purely speculative.